1. Field of the Invention
The present invention relates generally to the replacement of underground pipes, and more particularly to methods and apparatus for replacing fracturable pipes with new pipes which may be of the same size as, or larger than, the old pipes. Still more particularly, the present invention relates to methods and apparatus for replacing existing sewer pipes, water pipes, gas mains, or the like by first crushing the existing pipes inwardly to destroy them, then forcing the debris or shards of the destroyed pipe outwardly into the surrounding earth or other environment to form a bore of the appropriate size, and finally pulling the replacement pipe into the bore.
2. Background Art
It is often necessary to repair or replace underground pipes which have lost their fluid-carrying capacity or integrity for example through age, the actions of corrosive substances, or the effects of other deleterious conditions or hazards. One reason why repair or replacement is sometimes necessary is to prevent the leakage of the fluid into the surrounding earth or other environment. Such leakaqe could lead to contamination of the surrounding soil or subterranean potable water sources or supplies, for example in the case of underground sewer lines, or to contamination of the fluids carried within the underground pipes, for example in the case of underground water lines. Such leakage could also lead to potentially violent destructive conditions, placing property, health, or even lives imminently at risk, for example in the case of underground gas mains. If an underground natural gas main were to become corroded away, for example, allowing the gas to escape from the main, that could lead to an unwanted and potentially explosive accumulation of gases in a subterranean reservoir or other formation, or even in a building or other structure.
Another reason why repair or replacement is sometimes necessary is to restore the fluid-carrying capacity of the underground pipes. A sewer line which has become badly decomposed or broken up, for example, often cannot carry the volume of material for which it was designed. This can lead to temporary backups in the event the sewer system becomes deluged by an unusual event, such as a large storm, or eventually to complete blockages.
On technique used in the past for repairing or replacing underground pipes has been to excavate from above to provide access to the old pipes. Once excavated, the old pipes may be repaired or replaced as desired, and new pipes installed in place of the old ones, again as desired. This technique is usually time-consuming and expensive, however, involving as it does the duplication of effort in creating a new excavation at a site previously excavated, and for other reasons affecting the cost of the new excavation such as the depth at which the pipes are located, the subterranean environment of the pipes, and the surface conditions above the pipes. Sometimes this technique is unavailable as an option in a particular case even if desired, for example due to the presence of a surface structure such as a building through which an excavation cannot proceed.
One method of repairing underground pipes to keep them in service without completely excavating the pipes has been to install a liner within the pipes where necessary to restore the fluid-carrying integrity of the pipes. The sewer lines or the like can be viewed internally with remote television equipment to determine where the liners are necessary. The major problem with the so-called "slip lining" technique is that the liners have a smaller internal diameter ("ID") than the original pipes, thus reducing the capacity of the pipes. For example, an 8" ID pipe when lined may have an ID of only 6".
Another technique used in the past for replacing underground pipes has been to cut or slit them longitudinally by pulling a cutting tool through the pipes; expanding the resulting segments outwardly with an expanding tool, which may also comprise the cutting tool, to make room for the new pipe; and pulling the new pipe into the space thus created, typically behind and along with the expanding or expanding/cutting tool. Such a technique is useful particularly for pipes made of materials such as steel which do not normally fracture into irregularly-shaped pieces or shards when engaged by a blow or like impact. These techniques may be used to replace an old pipe with one of an equal or larger diameter, if desired. An example of this type of technique is disclosed in U.S. Pat. No. 4,903,406 to Schosek et al. That patent discloses a pipe splitter having a cutting wheel adapted for cutting a pipe, such as a black iron pipe, along a single longitudinal path when pulled through the pipe. An expander may be pulled through the split pipe for spreading the pipe apart, and anew pipe pulled into place trailing the expander. Another example of this type of technique is disclosed in U.S. Pat. No. 3,181,302 to Lindsay. The Lindsay apparatus is adapted to spit or cut the existing pipe longitudinally at two locations, for example into two halves, rather than at one location as in the Schosek '406 patent. Examples of other devices used in the past for cutting, ripping, or splitting pipes, casing, tubing, or the like are found in U.S. Pat. Nos. 642,367; 1,001,205; 1,519,882; 1,618,368; 2,502,711; 2,638,165; 2,834,106; 2,947,253; 2,983,042; and 3,023,040.
Another technique used in the past for replacing underground pipes with the same or larger diameter pipes, if desired, has been to burst them from the inside by pulling or pushing a bursting tool through the pipes; expanding the resulting pipe fragments outwardly with an expanding tool, which may also comprise the bursting tool, to make room for the new pipe; and pulling the new pipe into the space thus created, typically behind and along with the expanding or expanding/bursting tool. Such a technique is useful particularly for pipes made of materials such as concrete, tile, or cast iron, which normally fracture into irregularly-shaped pieces or shards when engaged by a blow or like impact. An example of a system utilizing this type of technique is disclosed in U.S. Pat. Nos. 4,505,302, 4,720,211, and 4,738,565 to Streatfield et al. The pipe bursting tool of the Streatfield patents is adapted to engage the interior to burst it, and to force the pipe fragments outwardly around the circumference of the tool to create a space for the new pipe, at least a portion of the outward forcing of the pipe fragments occurring at the same time the pipe is destroyed by the outwardly directed fracturing or bursting action.
U.S. Pat. No. 4,507,019 to Thompson discloses another pipe replacement system of the latter type, including a power system for imparting rotation as well as linear movement to an expansion and replacement mandrel as it is moved through the old pipe. The expansion and replacement mandrel of the Thompson system includes a plurality of hard metal boring buttons of a material such as tungsten carbide to score the internal surface of the existing pipe as the mandrel is rotated and forced through the pipe. The Thompson system, like the Streatfield system, engages the ID of the existing pipe to destroy it b initially fracturing it outwardly, i.e., by bursting it. The Streatfield and Thompson patents all disclose expanding the pipe fragments radially outwardly to create a large enough space for pulling in a replacement pipe of the same or larger diameter behind, and along with, their respective bursting tools.
Other systems of this type for replacing an existing pipe, that is, systems relying on bursting the existing pipe from the inside, are disclosed in U.S. Pat. No. 4,634,313; 4,648,746; 4,674,914; 4,693,404; 4,732,222; and 4,767,236.
Another technique for renewing an existing pipeline is disclosed in U.S. Pat. No. 4,886,396 to Akesaka. Akesaka discloses apparatus and methods for advancing a shield tunneling machine from one end of the existing pipeline to the other, thereby excavating the existing pipeline with rotating cutters, and placing a new pipeline in the excavated spot while the machine is advanced. The shield tunneling machine of Akesaka may have a diameter larger than the diameter of the existing pipe, so it may excavate not only the existing pipe but also some of the surrounding ground.
A self-propelled pneumatic burrowing device is disclosed in U.S. Pat. No. 4,100,980 to Jenne. The Jenne device includes an axially reciprocating percussion plunger disposed inside a tubular casing so as to strike a percussion head at the forward end of the casing, thereby advancing the device through the ground by crushing and/or displacing the material in the path of the device.